1. Field of the Invention
The invention relates to an internal combustion engine which includes an advanced vehicle system controller (VSC) that calculates the total engine power needed to meet the driver demand plus all accessory loads and independently schedules the engine speed and load operating point, with or without feedback of actual engine performance, to meet the total power demand.
2. Background Art
In an existing internal combustion engine including an advanced vehicle system controller (VSC), the VSC calculates the total engine power needed to meet the driver wheel power demand plus all accessory loads, and independently schedules the engine speed and load operating point, with or without feedback of actual engine performance, to meet the total power demand. By scheduling the most efficient engine speed and load operating point, the VSC may attempt to maximize fuel economy. Examples of powertrain systems which may involve VSCs include continuously variable transmission (CVT) and power split hybrid applications.
In an existing hybrid electric vehicle including such a VSC, the engine speed can flare up by 1,000 rpm when the air conditioner (A/C) compressor clutch engages. When the A/C compressor clutch disengages, the engine speed falls by 1,000 rpm. This engine speed cycling would typically occur at higher altitudes where the engine is running at wide open throttle (WOT). If the hybrid electric vehicle runs the engine at WOT at lower altitudes, then engine speed cycling at lower altitudes can also occur. The compressor clutch engaging and disengaging is driven by low and high pressure cut-out switches in the A/C system. Accordingly, the A/C compressor clutch cycles independently of the climate control panel's mode selector switch and the driver's accelerator pedal position. As such, the changes in engine speed are not associated with a driver input. Therefore, this engine speed behavior may be intrusive and disturbing to the operator of the vehicle.
In the existing hybrid electric vehicle, the engine speed flare up is a result of the VSC's response to a reduction in available engine brake power caused by the A/C compressor clutch engagement. Put another way, the VSC calculates the total engine power needed to meet the driver demand plus all accessory loads and independently schedules the engine speed and load operating point to meet the total power demand. The engaging of the A/C compressor clutch increases the accessory load, thus increasing the total power demand. When the engine is operating at WOT, in order to maintain the driver's requested wheel power output and the high voltage battery charge balance, the VSC must compensate for the power lost to the A/C system by raising the engine speed.
When the engine is not running at WOT, the VSC may respond to A/C cycling by adjusting the throttle position to increase or decrease the brake engine power as necessary. These throttle position adjustments are sufficient to make up the power consumed by the A/C system and the VSC does not need to increase the engine speed. However, at higher elevations, the VSC runs the engine at wide open throttle (WOT) frequently so that the VSC responds to A/C compressor clutch engagements by increasing the engine speed.
In general, any change to engine brake power not associated with a driver input can cause the VSC to respond with an intrusive engine speed change.
For the foregoing reasons, there is a need for a method for controlling an internal combustion engine including an advanced vehicle system controller that addresses these engine speed flare ups.